1. Field of the Invention
This invention relates to a method and apparatus for teaching individuals to estimate the size and attributes of objects; e.g., portions of food.
2. Description of the Related Art
Heart disease, stroke and diabetes are the three leading disease-specific causes of death in the US. Efforts to prevent these diseases or keep them in check have focused on diet, with or without exercise regimens, education and behavior modification programs.
Especially in the case of diabetes, prevention strategies center on diet. Obesity appears to aggravate the development of diabetes; and weight loss appears to reduce the risk of developing diabetes. In one study of obese individuals, after six years of follow-up, more than 50% of the subjects developed and an additional 30% showed impaired glucose tolerance. It has been known for more than 40 years that glucose tolerance can return to normal upon a reduction in body weight. Several recent studies demonstrate significant beneficial effects on carbohydrate and lipid metabolism without the necessity of obtaining ideal body weight. There would be an enormous positive effect if there were even moderate compliance with recommendations for a healthy diet.
The failure of the usual diet strategies is well known. A new technique for verifying actual food intake, the double water method has established the unreliability of self-reporting of food intake, especially by the obese. The doubly labeled water method measures integral CO2 production from the difference in elimination rates of deuterium and 18Oxygen from labeled body water. Validations against near continuous respiratory gas exchange have demonstrated that the method has a 2 to 8 percent precision depending on the isotope dose and the length of the elimination period. [Schoeller DA. Measurement of energy expenditure in free-living humans using doubly labeled water. J Nutr 1988;118:1278-89.] The doubly labeled water method is non-invasive and nonrestrictive, but very expensive. It identifies misreporting but it does not indicate the possible causes for the errors.
Two recent studies indicate the standard recommended procedure for learning to conform to a diet regimen. Analyzing the reasons for the failure of self reporting suggests the need for better methods and or better tools.
Long term studies were performed by Lichtman et al. with free-living subjects at the Beltsville Human Nutrition Research Center over the past 14 years. [Lichtman et al. Discrepancy between self-reported and actual caloric intake and exercise in obese subjects. N Engl J Med 1992;327:1893-8.] Although there had been a suspicion of systematic under-reporting of food intake, most of the published data records were small, which may account for the fact that they created little discussion. In 1990 a large study of 266 free living volunteers, with no health problems, on a weight maintenance diet was conducted. [Metz et al. What are people really eating? The relationship between energy intake derived from estimated records and intake determined to maintain body weight. Am J Clin Nutr 1991;54:291-5.]
The subjects were given an initial one hour period of instruction in measuring and estimating techniques. The subjects were instructed by registered dieticians in groups of ten or less. The diet questionnaire was explained, there was demonstration and practice in the use of measuring scales, spoons and cups. Instruction was given on estimating portion size without measuring devices for meals eaten away from home. The participants took the measuring devices home, and were expected to measure their food portions at home. The dieticians scrutinized the diet records in the presence of the subjects on a daily basis, weekends excepted, to resolve any questions as to quantity, incomplete records, or vague descriptions. The subjects recorded their food and drink intake daily for at least seven days. They were admonished not to change their habitual life styles, particularly their physical activity. All meals were provided, including snacks, and milk and sweetener for coffee or tea. It is to be noted that weekday breakfast and dinner was consumed at the center, and lunch was consumed at work, so that the weighing and measuring tools which were taken home were, presumably used only for weekend meals at home. The mean difference between recorded and determined intake was an under-reporting of approximately 18% with no significant difference for sex, age or weight of the subjects. [Metz et al]
These data agree with the recent study from the UK by Livingstone et al. in which one week dietary records of trained subjects were found to underestimate the energy expenditure by more than 20% in 18 subjects and as much as 50% in three subjects.
Despite the difference in the background of the Beltsville population versus the UK population the proportion of subjects underestimating their energy intake was 81% in Beltsville versus 84% in the UK study. Two different methods were used to estimate energy requirements, the measured intake for long term weight maintenance used in Beltsville versus the measurement of energy expenditure measured by the doubly labeled water method used in the UK study.
The study reported by Livingstone et al. reflects extreme care in the training of 31 subjects representing a wide range of ages occupations and socioeconomic status in Northern Ireland. [Livingstone et al. Accuracy of weighed dietary records in studies of diet and health. BMJ 1990;300:708-12.] For seven days each subject recorded the weight of items of food and fluid consumed and of leftovers. They were given scales, logbooks and written instructions including examples of completed forms. The day before the recording started each subject was given a detailed explanation and shown the cumulative weighing technique and then repeated the procedure in the presence of the investigator to insure that he or she was competent in the technique. The subject's progress in weighing foods was monitored and the records checked for completeness and accuracy. Subjects were instructed to record brand names of foods and to provide a complete description of the method of preparation, cooking, and recipes for composite dishes. These records were used to adjust for losses during cooking.
For foods and fluids eaten away from home, a description of the food, place of purchase, and the price were requested. When possible the corresponding portions of food were bought and weighed. But if this was not feasible, then estimated weights based on the average portion eaten by the subject was used. The researchers concluded that the observed discrepancies arose largely from inaccurate estimates of habitual energy intake due to conscious or subconscious changes in normal dietary patterns or under-reporting or both. The results closely replicated the previous year's measurements. Two different investigators were used in the two studies which strongly suggests that the bias is not due to the observer but is inherent in the method and the impact of the test on the subject. "Bias may be greater than is generally appreciated, consequently the seven day weighed record may lose accuracy in an attempt to increase precision." [Livingstone et al.]
Interviews were conducted with the subjects after the study in which they all emphasized that the weighing protocol had interfered with their normal eating behavior, and they had difficulty in maintaining motivation particularly in the middle of the measurement period. Having to weigh snacks was named as the most onerous and irritating aspect of the procedure, and subjects admitted having omitted or simplified some measurements.
The report notes that over half of the people invited to participate in the study declined to do so and that it was most difficult to recruit those subjects who had previously been found to have low energy intakes. The present study was therefore probably weighted in favor of more highly motivated and compliant subjects. And thus the bias is unlikely to be an overestimate of either the frequency or the degree of error that would exist in more representative study populations.
Livingstone et al. is characterized by rigorously trained investigators who maintained a high level of contact with subjects who had received more that the usual level of training. The Beltsville study indicates almost as much training and supervision. The subjects were all deemed capable of accurate weighing, measuring and recording. Both groups were considered highly motivated. Furthermore, it is unlikely that over eighty per cent of the subjects would consciously and consistently underreport food intake by around twenty per cent. Both studies make clear that even under carefully controlled circumstances the weighing, measuring, recording protocol is too complex and too intrusive.
In considering why dietary self reporting is so problematic it is perhaps useful to consider what skills are actually represented in asking subjects to keep a diary. One skill is the ability to accurately weigh and measure food. A second skill is recording these measurements. A third skill is the ability to judge the comparative size of objects. A fourth skill is to make the association between the visualization of the food in a measured container to the free form volume of food on a plate.
The Lichtman and Livingstone studies show that subjects who were taught weighing and measuring skills and how to enter the results in a log were judged by nutrition professionals to be adequately proficient in these skills, underestimated their food intake substantially. Since the subjects were judged to be highly motivated, the intrusiveness of the recording method is one likely source of the errors.
A few studies made the attempt to measure the ability of the subjects to estimate the size of objects. In a study of subjects with anorexia nervosa, it is reported that Yellowlees set up a videotape of five high energy foods and four neutral objects of similar size. [Yellowlees et al. Abnormal perception of food size in anorexia nervosa. BMJ 1988;296:1689-90.] The videotapes were made so that the portion of food or the object was initially shown as an image on the screen at one half of its actual size and increased steadily over a minute's duration to twice its actual size. The value of the magnification appeared in the lower right hand corner of the screen but was covered by a tab during the experiment. The images of food were alternated with the neutral objects. A dummy television screen was placed to the right of the real TV screen and a corresponding real object was placed in the middle of the dummy screen. Using a remote control, the subject was able to stop the videotape when the image was estimated to be the same size as the real object in the adjacent dummy screen. When the subject was satisfied with the result, the experimenter lifted the tab and recorded the value of the magnification. In a second experiment the object was removed after ten seconds, and the subject was required to choose the videotape image from what was remembered of the real object. In the third experiment the object was shown without reference to the videotape, and the subject was asked to indicate its width by drawing a straight line on a blank sheet of paper. Whether or not the object remained in view was not stated in the report. In the Yellowlees study no difference was found between the group with anorexia and the control group in their ability to measure the size of neutral objects. Both groups did, however, noticeably exaggerate the size of foods. The subjects with anorexia perceived food as 12% larger than the control subjects did in each experiment. This significant difference highlights the psychological component to food size estimation.
In the Lichtman study it is reported that the subjects were given some version of the Yellowlees test to determine the ability of the subjects and ten of the controls to accurately estimate portion size. The subjects were asked to estimate the overall size (the linear dimensions, and the volume and weight of various standard foods.) As in the Yellowlees study, the results were expressed as a percentage of the actual weight or volume. The scores for both groups were practically perfect. The percentage of actual portion size identified by the subjects was 98.+-.17 and for the controls was 96.+-.11. In contrast, these same subjects under-reported their actual food intake by an average 47.+-.16%; while the controls under-reported their energy intake by 19.+-.38%. This suggests that it is not the inability to judge size, per se, that causes the inaccuracy of estimation of dietary intake.
Another study which suggests that it is not the inability to judge size, per se, which causes the under-reporting is reported by Lansky et al. [Lansky et al. Estimates of food quantity calories: errors in self-report among obese patients. Am J Clin Nutr and 1982;35:727-32.] In this study an attempt was made to directly test the assumption that size cues are affected by the size of the plate on which the food portions are presented. Five foods on large plates, and five foods on small plates were presented, all of the same size portion. Except for one food, cottage cheese, there was no significant difference between the estimates made for large and small plates. For cottage cheese, the subjects estimated that the small plate had fewer calories in its portion than the large plate. These subjects received no special training. They were asked to estimate the quantity of ten foods by weight or fluid ounces and then to estimate calories using a chart. These obese, dieting subjects underestimated quantity by 63.9 per cent and calories by 53.4 per cent [Lansky et al].
One of the implicit assumptions in the weighing, measuring and reporting protocol is that the individual will be able to make the association between the size of the food portion in the measuring utensil and the food encountered in a natural situation. The above analysis indicates that this failure of association may actually be the most significant contributor to the reporting error margins.
There is a known method used in teaching nutrition which addresses this issue. Realistic scale models of food portions as they appear on a plate are made out of composite materials. They are very expensive to make and a different object must be made for each different portion size for each food. The cost and unwieldy nature of this method keeps it from widespread use and testing. It is not a method designed for home use and storage problems would make it very intrusive.
The scale model method at least addresses the issue of the relationship of a food portion to a realistic visually perceived size. Other systems presuppose an intermediate step of numerical calculation by the individual. The most common source of nutrition information is printed on the labels of processed food which provides, inter alia, calories, fat, protein and carbohydrate content for each food portion in grams or milligrams, and the U.S. Recommended Daily Allowance of common nutrients for each food portion expressed in percentages. The size of the portion, however, is determined by the manufacturer without regard to any consistency from product to product. Frequently it is impractical to calculate a single portion without emptying the entire contents of the package.
A system for reducing the amount of numerical calculation is the "Exchange Lists For Meal Planning" promulgated by the American Diabetes Association, Inc. and The American Dietetic Association. This system utilizes six groupings of food: starch/bread, vegetables, milk, meat and substitutes, fruit, and fat. Within each group different sizes of portions of respective different kinds of food will provide the same number of calories. For example, in the starch group 1/2 cup of pasta and 1 slice of bread (each being one starch exchange unit,) will each provide 80 calories; and in the meat group 1 ounce of cooked poultry, fish or meat and 1/4 cup of cottage cheese (each being one meat exchange unit,) will each provide 75 calories. A healthy daily diet of 1200 calories per day, can consist of 4 starch units, 5 meat units, 2 vegetable units, 2 fruit units, 2 skim milk units, and not more than 3 fat units per day. The distribution (and quantity) of the calories and groups over the several meals of the day is left to a dietician to prescribe (e.g., 25%, 35% and 45%,) for the specific needs of the specific patient. Serving sizes are taught by weighing or measuring out the food, e.g., ounces, grams, cups, and teaspoons.
Weighing and measuring is at the heart of all known systems for calculating the size of a food portion. The calculation is then associated with a visualization of the size of the portion either associated with the means of measuring or, as an additional step, as it would appear in a real life setting. The goal for the individual using the system is to recognize the total correct portion sizes for a customized best diet for that individual.
This invention offers a direct method for learning portion sizes appropriate to each individual, a non-intrusive method of remembering and checking the correct size of a portion, and a sense of the relative portion sizes appropriate to the individual's total diet.